Re: [tip:x86/boot] x86/boot: Early parse RSDP and save it in boot_params

[Chao Fan <fanc.fnst@cn.fujitsu.com>]

On Mon, Feb 11, 2019 at 01:22:20AM +0100, Borislav Petkov wrote:
>On Fri, Feb 08, 2019 at 10:53:22PM +0100, Borislav Petkov wrote:
>> On Fri, Feb 08, 2019 at 12:44:51PM -0800, Guenter Roeck wrote:
>> > Yes, the kernel boots if I comment out that function and have it return 0.
>> 
>> Thanks, this localizes the issue significantly.
>
>Some observations:
>
>                } else {
>                        efi_config_table_32_t *tmp_table;
>
>                        tmp_table = config_tables;
>                        guid = tmp_table->guid;			<--- *
>                        table = tmp_table->table;
>                }
>
>It blows up at that tmp_table->guid deref above. Singlestepping through
>it with gdb shows:
>
># arch/x86/boot/compressed/acpi.c:114: 			guid = tmp_table->guid;
>	movq	(%rdi), %rax	# MEM[(struct efi_config_table_32_t *)config_tables_37].guid, guid
>	movq	8(%rdi), %rsi	# MEM[(struct efi_config_table_32_t *)config_tables_37].guid, guid
># arch/x86/boot/compressed/acpi.c:115: 			table = tmp_table->table;
>	movl	16(%rdi), %r10d	# MEM[(struct efi_config_table_32_t *)config_tables_37].table, table
>	jmp	.L30	#
>
>and %rdi has:
>
>	rdi            0x630646870
>
>which is an address above 4G but we're using a 32-bit EFI BIOS.
>
>Which begs the question whether EFI system tables can even be mapped at
>something above 4G with a 32-bit EFI and whether that could work ok.
>Hmm.

Thanks for your help. As you said, I am not wure whether 32-bit EFI can
map table address above 4G.
If the map method has problem, I think adding a check here can work.

Thanks,
Chao Fan

>
>Lemme add Ard and mfleming for insight here.
>
>Thx.
>
>-- 
>Regards/Gruss,
>    Boris.
>
>Good mailing practices for 400: avoid top-posting and trim the reply.
>
>